Broadly speaking, this invention relates to covers for use on various types of machines, such as compressors, in order to dampen and reduce noise emitted by such machines. More specifically, the invention relates to relatively rigid laminated covers tailored to the approximate shape of the machine to be covered, which can readily be slipped over the machine and thereafter closed to encase the machine in a sound absorbent material.
It has been found that prolonged exposure to noise generated by various types of machines, such as compressors, can have harmful effects upon the persons so exposed. For this reason, various types of covers and housings have been developed in the prior art to be applied about such machines to reduce the noise generated thereby.
See, for example, U.S. Pat. No. 3,896,897 issued to E. O. Hillbush, Jr. on Jul. 29, 1975 and U.S. Pat. No. 2,949,975 issued to W. A. Plummer on Aug. 23, 1960, both of which patents disclose highly flexible, laminate, blanket-like covers adapted for wrapping about the body of a pneumatic tool such as a jack hammer or air drill. The cover of Hillbush, Jr. includes an inner layer of porus or open cell polyurethane sponge, a middle layer of lead, tin, bismuth, zinc, copper, or aluminum sheet which is annealed sufficiently so that it can be shaped around a pneumatic tool body and so that it will not mechanically resonate at the vibratory frequency of the tool. The subject cover also includes an outer layer of cloth, such as neoprene coated with nylon, or other elastomeric material such as rubber, butyl or acrylonitrile, which can withstand the type of shock and distortion to be encountered when applied to such tools.
The cover of Plummer includes an inner jacket of flexible material having a main body layer of sound absorbing material such as comminuted wood fibers overlayed with a layer of reinforcing fibrous material such as spun fiberglass. The two layers of wood fibers and fiberglass are held between inner and outer fabric cover sheets.
The covers of both of these patents are relatively complex laminate structures and are not sufficiently rigid to retain a given shape separate and apart from the tool body about which they are to be wrapped. Also, the wrapping of such a highly flexible sound absorbent cover about machinery is cumbersome. By contrast, it would be desirable to have a cover which is sufficiently rigid to retain a desired form, yet still be flexible and resilient enough to be bent both for slipping over the top of a machine, for ease of installation and removal, and for laying open for stacking and nesting any number of such covers successively, one within another, for saving space in the shipping and storage of quantities thereof.
By means of my invention, these and other shortcomings of prior art muffler covers are substantially overcome.